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(f) Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into
several crop plants as cotton.
(g) Most Bt toxins are insect-group specific. The toxin is coded by a gene named cry, e.g. the
proteins encoded by the genes cry IAc and cry IIAb control the cotton bollworms and cry IAb
controls corn borer.
(vi) Pest resistant plants are developed by using biotechnological processes.
(a) A nematode Meloidogyne incognita infects the roots of tobacco plants, which reduces
the production of tobacco.
(b) RNA interference (RNAi) process is used for cellular defence. It involves silencing of a
specific mRNA due to a complementary dsRNA. It occurs in all eukaryotic organisms as a
method of cellular defense.
(c) dsRNA binds and prevents translation of the mRNA (silencing).
(d) The source of this complementary RNA could be from an infection by viruses having RNA
genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.
(e) Agrobacterium vectors are used to introduce nematode-specific genes into the host
plant. It produces both sense and anti-sense RNA in the host cells.
(f) These two RNAs are complementary to each other and forms a double stranded RNA
(dsRNA) that initiate RNAi and hence, silence the specific mRNA of the nematode.
(g) The parasite cannot survive in transgenic host, expressing specific interfering RNA. The
transgenic plant thus, gets itself protected from the parasite.
4. Biotechnological applications in medicine have made immense impact in the area of
healthcare by enabling the mass production of safe and more effective therapeutic drugs.
(a) The recombinant therapeutics do not induce unwanted immunological responses as in
case of similar products isolated from non-human sources.
(b) Currently, about 30 recombinant therapeutics have been approved for human use over
the world. In India, 12 of these are presently being marketed.
I. Genetically engineered insulin leads to sufficient availability of insulin for the
management of adult-onset diabetes.
(a) Insulin used for diabetes was earlier extracted from the pancreas of slaughtered cattle
and pigs. This caused allergy or other reactions in some patients.
(b) Insulin consists of two short polypeptide chains, i.e. chain-A and B, linked together by
disulphide bridges.
Maturation of proinsulin into insulin (simplified)
(c) In mammals, insulin is synthesised as a prohormone (needs to be processed before it
becomes a fully mature and functional hormone) which contains an extra stretch called the
C-peptide.